{
  "id": "gdt",
  "title": "GD&T characteristic symbols — the 14 geometric controls",
  "url": "https://nxtolerance.com/data/gdt.json",
  "page": "https://nxtolerance.com/tools/",
  "source": {
    "name": "Engineering tolerance standards reference data",
    "publisher": "SuperNX / nxtolerance.com",
    "standards": "ASME Y14.5 characteristic symbols (ISO 1101 uses an equivalent set)",
    "note": "Values compiled from the published standard tables and cross-checked against multiple independent public references; see the verification log in the source repository.",
    "method": "sym = unicode glyph approximation; datum = whether the control requires datum references."
  },
  "symbols": [
    {
      "id": "straightness",
      "name": "Straightness",
      "sym": "—",
      "cat": "form",
      "datum": false,
      "desc": "Each line element of the feature stays within a tolerance zone of two parallel lines."
    },
    {
      "id": "flatness",
      "name": "Flatness",
      "sym": "⏥",
      "cat": "form",
      "datum": false,
      "desc": "The surface stays within a zone between two parallel planes."
    },
    {
      "id": "circularity",
      "name": "Circularity (roundness)",
      "sym": "○",
      "cat": "form",
      "datum": false,
      "desc": "Each cross-sectional circle stays within a zone between two concentric circles."
    },
    {
      "id": "cylindricity",
      "name": "Cylindricity",
      "sym": "⌭",
      "cat": "form",
      "datum": false,
      "desc": "The cylindrical surface stays within a zone between two coaxial cylinders — controls roundness, straightness and taper together."
    },
    {
      "id": "profile-line",
      "name": "Profile of a line",
      "sym": "⌒",
      "cat": "profile",
      "datum": "optional",
      "desc": "Each line element of a profile stays within a uniform zone along the true profile."
    },
    {
      "id": "profile-surface",
      "name": "Profile of a surface",
      "sym": "⌓",
      "cat": "profile",
      "datum": "optional",
      "desc": "The whole surface stays within a uniform zone around the true profile — can locate, orient and size at once."
    },
    {
      "id": "perpendicularity",
      "name": "Perpendicularity",
      "sym": "⊥",
      "cat": "orientation",
      "datum": true,
      "desc": "Surface or axis stays within a zone at exactly 90° to the datum."
    },
    {
      "id": "angularity",
      "name": "Angularity",
      "sym": "∠",
      "cat": "orientation",
      "datum": true,
      "desc": "Surface or axis stays within a zone at a specified non-90° angle to the datum."
    },
    {
      "id": "parallelism",
      "name": "Parallelism",
      "sym": "∥",
      "cat": "orientation",
      "datum": true,
      "desc": "Surface or axis stays within a zone parallel to the datum."
    },
    {
      "id": "position",
      "name": "Position",
      "sym": "⌖",
      "cat": "location",
      "datum": true,
      "desc": "The feature axis/center stays within a zone (often Ø at MMC) around the theoretically exact location."
    },
    {
      "id": "concentricity",
      "name": "Concentricity",
      "sym": "◎",
      "cat": "location",
      "datum": true,
      "removedIn": "ASME Y14.5-2018",
      "desc": "Median points of diametrically opposed elements stay within a cylindrical zone around the datum axis."
    },
    {
      "id": "symmetry",
      "name": "Symmetry",
      "sym": "⌯",
      "cat": "location",
      "datum": true,
      "removedIn": "ASME Y14.5-2018",
      "desc": "The median points of opposed feature surfaces stay centered on the datum center plane."
    },
    {
      "id": "runout-circular",
      "name": "Circular runout",
      "sym": "↗",
      "cat": "runout",
      "datum": true,
      "desc": "Each circular element stays within runout limits measured per revolution about the datum axis."
    },
    {
      "id": "runout-total",
      "name": "Total runout",
      "sym": "↗↗",
      "cat": "runout",
      "datum": true,
      "desc": "The entire surface stays within runout limits across a full sweep about the datum axis."
    }
  ],
  "disclaimer": "Engineering reference values for design and education — verify against the current standard revision (ISO 286-1:2010, ISO 2768-1:1989, ASME Y14.5) before issuing production drawings.",
  "license": "Standard reference data. Free to use and cite with attribution to nxtolerance.com.",
  "version": "2026-10-07"
}